Chemical vapor deposition (CVD) is a method of forming a layer of material on a substrate, such as an epitaxial layer on a silicon wafer, wherein deposits are produced by heterogeneous gas-solid or gas-liquid chemical reactions at the surface of the substrate. One form of structure for achieving CVD processing is a rotary disc reactor in which a number of stacked parallel graphite discs serving as susceptors carry silicon wafers on one or both sides of the discs is described in U.S. Pat. Nos. 4,062,318 and 4,082,865 issued Dec. 13, 1977 and Apr. 4, 1978, respectively. The stacked susceptor structure is enclosed within a quartz tube surrounded by an RF induction heating coil. A gas manifold is provided with a plurality of gas nozzles for the injection of the gas into peripheral proportions of the stacked discs. The gas manifold and thus the nozzles in prior art rotary reactor structures are oscillated to spread the gas plume uniformly over the surface of the susceptor discs and wafers carried on the discs. The RF coil inductively heats the graphite discs by inductive process through the wall of the quartz tube.
The gas carrying the material is conveyed into the reaction chamber by means of gas tube manifolds that are provided with slots, openings or nozzles that are positioned to generate gas streams that flow over the surface of the wafers or substrates. In typical rotary disc reactor apparatus, the gas manifold tubes are oscillated to sweep a gas stream over the rotating wafers or substrates. See, for example, U.S. Pat. No. 4,082,865 for a gas manifold using a single tube with nozzles for generating the gas streams. See also U.S. Pat. No. 4,401,689 for apparatus using a coaxial gas manifold tube means wherein the gas is first introduced into the chamber through an inner tube and then passed to an outer tube or shroud which provides a gas stream through a series of holes or slots while the tube is oscillated back and forth over the surface of the wafers or substrates.
The use of slotted, oscillating gas manifolds have been used with certain degrees of success with wafers of limited size, on the order of 21/2 to 3 inches in diameter. However, the uniformity of thickness and the growth rates of such single slot gas manifold tubes are limited by the maximum gas velocity that they can handle without developing turbulence and poor deposition properties.